This invention relates to the medicated resin moldings which can gradually or slowly release the drug incorporated therein (hereinafter referred to as slow-releasing medicated resin moldings) and a process for producing such medicated resin moldings. More particularly, the invention relates to said slow-releasing medicated resin moldings characterized in particular by their capability of retaining a large quantity of drug and releasing the drug gradually at a constant rate, and a process for producing such slow-releasing medicated resin moldings.
A technique has been known for effecting gradual or slow release of a drug from a molding comprising a medicated resin composition prepared by uniformly incorporating a drug in a plastic resin by kneading. According to this technique, however, since the drug is released out to the ambience from the surface of the resin molding with the lapse of time and the drug release rate lowers as the drug content in the resin molding decreases, it was difficult to maintain release of the drug at a constant rate. Also, the maximal amount of a drug compatible with resin, although variable depending on the type of resin and drug used, is usually as low as about 0.1 to 5% by weight in the case of thermoplastic resins, so that constant release of the drug over a prolonged period of time could not be expected of the conventional medicated resin moldings. Even if a drug was blended in a large amount, such as exceeding the saturation dissolution rate, in the resin composition, it was still unable to realize long-time constant release of a drug because, in such a case, there would occur bleeding of the drug or mass release of the drug in the early time of use.
The present inventors have pursued studies in search of a drug slow-releasing technique which makes it possible for a molding to contain a large amount of drug without causing bleeding and also enables release of a drug at a constant rate over a prolonged period of time. As a result, the inventors found that a slow-releasing medicated resin molding capable of retaining a drug at a high content and releasing it at a constant rate can be obtained by making a medicated porous body from a resin composition comprising a resin, a filler and a drug in an amount exceeding the saturation dissolution rate for said resin by means of mono- or biaxial stretching. The present invention was achieved on the basis of this finding.
Thus, in accordance with the present invention, there are provided:
1. A slow-releasing medicated resin molding, wherein a drug is contained in a porous resin molding obtained by stretching 1.1-10 times a resin composition comprising 100 parts by weight of a thermoplastic resin and 50 to 400 parts by weight of a filler, the amount of the drug is not less than the saturation dissolution rate for the thermoplastic resin.
2. A process for producing a slow-releasing medicated resin molding, which comprises stretching 1.1-10 times mono- or biaxially a resin composition comprising 100 parts by weight of a thermoplastic resin, 50 to 400 parts by weight of a filler and a drug in an amount not less than the saturation dissolution rate for the thermoplastic resin, whereby the composition is made porous.
3. A process for producing a slow-releasing medicated resin molding, which comprises stretching 1.1-10 times mono- or biaxially a resin composition comprising 100 parts by weight of a thermoplastic resin and 50 to 400 parts by weight of a filler, wherein stretching is conducted in a state where said resin composition is immersed in or applied with a drug or its solution to make the composition porous.
4. A process for producing a slow-releasing medicated resin molding, which comprises impregnating the porous resin molding obtained by stretching 1.1-10 times mono- or biaxially a resin composition comprising 100 parts by weight of a thermoplastic resin and 50 to 400 parts by weight of a filler with a drug in an amount not less than the saturation dissolution rate for the thermoplastic resin.
5. A vermin control method using a slow-releasing medicated resin molding which is a porous body obtained by stretching 1.1-10 times a resin composition comprising 100 parts by weight of a thermoplastic resin and 50 to 400 parts by weight of a filler, and adding thereto at least one insecticide selected from the group consisting of pyrethroids, methoxydiazone and pyriproxyfen in an amount not less than the saturation dissolution rate for the thermoplastic resin.